Explanation
Correct answer: D.
Choice D is the best answer. “For example” logically signals that the information in this sentence—that resins quickly seal wounds to help prevent harmful insects and fungi from entering trees—provides a specific example to support the previous sentence’s claim about resins playing several important roles in maintaining tree health.
Why the other choices are wrong
Choice A
Choice A is incorrect because “however” illogically signals that the information in this sentence contrasts with the previous claim about resins playing several important roles in maintaining tree health. Instead, the sentence provides a specific example of one such role.
Choice B
Choice B is incorrect because “regardless” illogically signals that the information in this sentence is true despite the previous claim about resins playing several important roles in maintaining tree health. Instead, the sentence provides a specific example of one such role.
Choice C
Choice C is incorrect because “next” illogically signals that the information in this sentence is the next step in a process. Instead, the sentence provides a specific example to support the previous claim that resins play several important roles in maintaining tree health.